Lithium-ion (Li-ion) or lithium-polymer (Li-polymer) batteries are relatively new rechargeable batteries that may be used in systems that need to maximize run time. Typically, these batteries are configured as battery arrays, packs, or strings. The battery arrays, packs, or strings may include two cells (e.g., for consumer products such as camcorders or cameras), or up to four or more cells (e.g., for high-end notebook computers, automobile, aircraft). These multi-cell arrays, packs, or strings can be coupled in series and a number of series cell strings can be connected in parallel.
In multi-cell batteries, problems may arise due to differences in the characteristics of the individual cells, i.e., cell capacities. The difference in the cell ampere-hour (Ah) capacities is referred to as cell imbalance. In a new battery, the cells should be well balanced. Cell imbalance may develop, however, due to aging or other causes, such as, for example, insertion of different grade cells due to repair, battery misuse or differences in the active materiel quality of the cells at the time of cell manufacturing.
Because of these and other problems resulting from cell imbalance, cell balancing techniques are needed to equalize the charge on every cell and prevent individual cells from becoming over stressed. However, few techniques exist for diagnosing and/or predicting a cell imbalance condition for these batteries. Thus, there is a need to overcome these and other problems of the prior art and to provide a method and a system for diagnosing and/or determining impending cell imbalance of a battery, a battery array, pack, or string.